Solenoid plunger magnet and its use as print hammer in a print hammer device

ABSTRACT

A solenoid plunger magnet system is disclosed, preferably to be used as print hammer in a print hammer device. Known solenoid plunger magnets have in the exciting coil a first interferric gap as working interferric gap and a second interferric gap outside the exciting coil as loss interferric gap. The magnetic lines of force at the second gap are lost as moving forces for the solenoid plunger. The purpose of the invention is to increase the magnetic force of solenoid plunger magnets by using the second gap as well for generating forces, without affecting the generation of forces at the inner gap. For this purpose, a male taper control is arranged at the outer gap, which has a cylindrical shape and the usual length of loss gaps. A considerable increase of the magnetic force is thus achieved.

BACKGROUND OF THE INVENTION

The invention relates to a solenoid plunger magnet and to its use as aprint hammer in a print hammer device.

FIG. 1 shows a solenoid plunger magnet 5 as it is known from the earlydays of the magnetism art in the form of a blunt solenoid plunger 1which is pulled against a flat counter-pole 2 of a yoke 3. The workingair gap 4 of this solenoid plunger magnet 5 equals the length of travelof solenoid plunger 1. The result is a steeply rising tractive forcecurve which, particularly for long travel paths, becomes so weak at thebeginning, that it is hardly possible anymore to utilize it.Furthermore, the solenoid plunger magnet 5 also has a second air gap 6,also called the loss air gap since it contributes nothing to the thrustof solenoid plunger 1. The high striking force of solenoid plunger 1against counter-pole 2 also inevitably reduces its service life.

Therefore, the configuration of the air gaps so as to realize a maximumof performance and service life is very decisive. By appropriatelydesigning the geometry of the plunger and of the counter-poles, it ispossible to influence the characteristics over a broad range and thus toadapt them to the intended purpose. For this reason, the operating airgap is configured according to the desired lines of magnetic flux whilethe loss gap is configured in such a manner that it has the lowestpossible magnetic resistance but does not generate forces which move inthe direction toward solenoid plunger 1.

DE-OS 2,636,985 discloses a solenoid plunger system in which the secondair ga is also utilized to generate magnetic forces. However, theconfiguration of the outer air gap disclosed there is not meaningfulbecause it doubles the overall air gap length and thus results in areduction of magnetic flux and a reduction of the magnetic forces in thefirst air gap, the working air gap.

SUMMARY OF THE INVENTION

It is the object of the invention to configure a solenoid plunger magnetin such a way that the inner air gap and the outer air gap both serve togenerate forces without the overall air gap length being extended overthat customary for a solenoid plunger magnet.

The solenoid plunger magnet according to the invention, with the sameexterior dimensions and the same electrical data as the prior artmagnets, realizes an increase in magnetic forces up to 200%. Theconventional means for realizing the desired magnetic forcecharacteristic remain fully available for the inner air gap.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantageous features of the invention will become apparent inthe detailed description of the embodiments and the following drawings.

FIG. 1 a solenoid plunger magnet according to the prior art;

FIG. 2 the geometry of the plunger and the counter-pole at the inner airgap with external cone control;

FIG. 3 the geometry of the plunger and the counter-pole at the inner airgap with internal cone control;

FIG. 4 the geometry of the plunger and the counter-pole at the outer airgap with external cone control;

FIG. 5 the geometry of the plunger and the counter-pole at the outer airgap with internal cone control;

FIG. 6 the solenoid plunger magnet with internal cone control at theinner air gap and external cone control at the outer air gap;

FIG. 7 the magnetic flux lines at the outer air gap according to theprior art of FIG. 1;

FIG. 8 the magnetic flux lines in the outer air gap for a solenoidplunger magnet according to FIG. 6;

FIG. 9 force-travel curves for the solenoid plunger magnets according toFIGS. 1 and 6; and

FIG. 10 a solenoid plunger magnet with external cone control at theinner and outer air gap.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will now be described in greater detail with reference toembodiments thereof. In order to optimize the geometry of the plungerand counter-pole for the purpose of generating greater magnetic forces,FIGS. 2 and 3 illustrate examples for the configuration of the inner airgap. In FIG. 2, the plunger 7 is cylindrical, with the yoke 8 having acylindrical recess 9 and a conically configured exterior face 10 inorder to provide for external cone control. In this type of magnet, themagnetic force characteristic extends horizontally. FIG. 3 provides forinternal cone control in which case the solenoid plunger 11 has aconically configured exterior face 12 and dips into a correspondinglyshaped recess 13 of yoke 14. In this embodiment, the magnetic forcecharacteristic is progressive.

FIGS. 4 and 5 show possible embodiments of the outer air gap, with FIG.4 depicting an external cone control. Here, yoke 15 has a cylindricalrecess 16 including an inwardly projecting stop 17 for the free end 18of the cylindrical portion of solenoid plunger 19. In a known manner,solenoid plunger 19 has an internal cone 20.

According to FIG. 5, the outer air gap can also be controlled by way ofan internal cone control, with the yoke 21 having a conical exteriorface 22 and an abutment face 23 which can be charged by an abutment face24 on plunger 26. In a known manner, solenoid plunger 26 has an internalcone 25.

FIG. 6 shows a solenoid plunger magnet 43 for use as print hammer in aprint hammer device, with a solenoid plunger 26 being fixed to acylindrically configured guide member 31 composed of a non-magneticmaterial and being displaceably mounted in a bearing bore 30 of a yoke27. The inner air gap 44, seen in the axial direction, liesapproximately in the center of an excitation coil 46 which is fastenedin a known manner by means of a coil mount 47 on a cylindrical extension48 of yoke 27. The inner air gap 44 is formed by an inner cone control,with the exterior face 33 extending toward the coil axis when excitationcoil 46 is excited having a cone angle of less than 10°. This conicalouter face 33 dips into a conical recess 34 serving as counter-poleuntil the free end 35 of plunger 26 lies against the base face 36 ofyoke 27. Yoke 27 is composed of an inner member 29 including a bearingbore 30 and a cylindrical extension 48 and of a hollow cylinder 28 whichis fixed to member 29, with member 29 as well as hollow cylinder 28being composed of a high permeability material.

Guide member 31 includes a stop member 35 which, by way of aspring-tensioned lever having a hammer head, charges the type facespokes of a daisy wheel (not shown). This non-illustratedspring-tensioned lever sets guide member 31, which has been charged inthe direction of arrow 50, back into its starting position onceexcitation coil 46 is no longer excited, with a damping member 51 ofguide member 31 lying against yoke 27. This reliably avoids noisesduring resetting of guide member 31 into the starting position.

The outer air gap 45 is cylindrical in shape and is provided with anexternal cone control, with hollow cylinder 28 having a set-backcylindrical circumferential face 39 and plunger 26 having a cylindricalexterior face 28 to enable it to be immersed. The distance between thecircumferential face 39 and exterior face 38 is about 0.15 mm and thuscorresponds to the value of a normal loss air gap. Within cylindricalexterior face 38, plunger 26 is provided with a cavity 48 whose internalcircumferential face 37 is conical so as to form an external conecontrol. The circumferential lines of this cone extend from the outeredge 42 to the bottom face 49 of cavity 48 in such a manner that theyintersect the coil axis in a direction opposite to the direction ofmovement of solenoid plunger 26 when excitation coil 46 is excited. Thediameter of the outer air gap 45 has a ratio of approximately 1:1 to thediameter of the exterior diameter of excitation coil 46. Moreover, theouter face 38 forming the outer air gap 45 and the inner circumferentialface 39 at plunger 26 and yoke 27 are provided with edges 41, 42 asregions of denser magnetic flux which augment the forward thrust ofsolenoid plunger 26 at the beginning of its movement.

FIG. 8 shows the favorable path of the magnetic flux lines at the outerair gap at the transition from yoke 27 to solenoid plunger 26. FIG. 7shows the corresponding magnetic flux lines at outer air gap 54 of ayoke 53, the loss air gap. It can here be seen that the flux lines donot effectively support the movement of solenoid plunger 52. This FIG.also clearly shows the stray flux at the loss gap.

FIG. 9 shows the force-travel characteristics of solenoid plungermagnets whose inner and outer air gaps are configured according to FIGS.7 and 8. The dashed curves show the flux lines for solenoid plungermagnets according to FIG. 7 which have a working air gap and internalcone control while the solidly drawn curves relate to solenoid plungermagnets according to FIG. 8 which have two working air gaps. Thedifferences in performance between solenoid plunger magnets having oneand two working air gaps are clearly noticeable. In each case, theexcitation coil was operated at current intensities of 1 A and 1.5 A foron-periods of 40% and 10%.

A horizontal magnetic force characteristic can be realized with asolenoid plunger magnet system according to FIG. 10 in which the innerair gap 55 as well as the outer air gap 56 are cylindrical. Exteriorfaces 57, 58 at plunger 59 and the counter-pole faces at yoke 62 arecylindrical, with the rear face 63 of counter-pole face 60 and the rearface 64 of exterior face 58 being conical. In this way, the solenoidplunger magnet is given an external cone control at its inner (55) aswell as its outer air gap 56, thus realizing the generation of uniformforces over the entire travel path. Additionally, the solenoid plungermagnet according to FIG. 10 also includes an excitation coil 65 and areset spring 66 for solenoid plunger 59.

With the same external dimensions and the same electrical values, theproposed magnet system permits an increase of magnetic forces up to200%.

I claim:
 1. A solenoid plunger magnet comprising an excitation coil, a solenoid plunger partially projecting into this coil and a yoke of a high permeability material configured to serve as a flux guiding means for forming, together with the solenoid plunger, a path of magnetic flux for the magnetic field generated by the excitation coil, the magnet further being provided with a central recess for guiding a non-magnetic guide member along the plunger, with a first air gap being provided within the coil, when the solenoid plunger is in its starting position, and a second air gap outside the coil between a face of the solenoid plunger and a respectively adjacent, correspondingly configured counter-face of the yoke, characterized in that the faces facing the air gaps at the solenoid plunger and counter-faces of the yoke are configured in such a manner that at least one of the two air gaps is cylindrical and has an external cone control; and that the magnetic flux in both air gaps is utilized for conversion into the desired motion force component for the solenoid plunger, the faces facing the outer air gap are cylindrical, with the plunger being provided with a cavity within the cylindrical exterior face, and when seen in the direction opposite to the direction of movement of the solenoid plunger, the inner circumferential face of the cavity extends conically toward the coil axis from the outer edge to the bottom face of the cavity when the coil is excited so as to form an external cone control, and the outer and inner circumferential faces forming the outer air gap are provided with edges configured as regions of denser magnetic flux in order to augment the thrust of the plunger.
 2. A solenoid plunger magnet according to claim 1, wherein the outer air gap has an internal cone control, with exterior faces extending toward the coil axis in the direction of movement of the solenoid plunger when the coil is excited enclosing a cone angle of less than 10°.
 3. A solenoid plunger magnet according to claim 1 wherein when viewed in the axial direction, the inner gap lies approximately in the center of the excitation coil.
 4. A solenoid plunger magnet according to claim 1, wherein the faces of the plunger facing the inner air gap and the counter-face at the yoke in the form of a recess are conical so as to form an internal cone control.
 5. A solenoid plunger magnet according to claim 1, wherein the diameter of the outer air gap has a ratio of approximately 1:1 to the diameter of the coil.
 6. A solenoid plunger magnet according to claim 1, wherein the yoke has a cylindrical shape and is provided with a central bearing bore in which a guide member that is fixed to the plunger is displaceably mounted.
 7. A solenoid plunger magnet according to claim 6, wherein both air gaps are cylindrical.
 8. A solenoid plunger magnet according to claim 7, wherein the plunger and the yoke have external cones.
 9. A solenoid plunger magnet comprising:a coil for generating a magnetic field; a solenoid plunger having a cavity and partially projecting into said coil for providing a first air gap in said coil when said solenoid plunger is in a starting position and a second air gap outside said coil, said solenoid plunger including:a first plunger face facing the first air gap; a second cylindrical outer plunger face, the cavity being inside said second cylindrical outer plunger face; a bottom plunger face partially forming the cavity; a plunger edge adjacent to said second cylindrical outer plunger face; and an inner circumferential plunger face extending conically with respect to the coil axis from said plunger edge to said bottom plunger face in an external cone shape; a non-magnetic guide member connected to said solenoid plunger; a yoke of high permeability material and supporting said coil for forming together with said solenoid plunger a path of magnetic flux, and for forming, together with said second cylindrical outer plunger face, the second air gap outside said coil, said yoke including:a first yoke counter-face facing the first air gap; a second cylindrical inner yoke counter-face adjacent to an corresponding to said second cylindrical outer plunger face, the second air gap being provided between said second cylindrical inner yoke counter-face and said second cylindrical outer plunger face; a central recess for guiding said non-magnetic guide member along the coil axis; and a yoke edge adjacent to said second cylindrical inner yoke counter-face for providing dense magnetic flux in order to augment thrust of said plunger, wherein the magnetic flux in the first and second air gaps produces a desired motion of said solenoid plunger.
 10. A solenoid plunger magnet according to claim 9, wherein said yoke has a cylindrical shape and includes a central bearing bore, said guide member being displaceably mounted in said central bearing bore of said yoke.
 11. A solenoid plunger magnet according to claim 10, wherein the first and second air gaps are cylindrical.
 12. A solenoid plunger magnet according to claim 11, wherein said plunger and said yoke have external cones.
 13. A solenoid plunger magnet according to claim 9, wherein said first yoke counter-face and said first plunger face extend toward the coil axis in the direction of movement of said solenoid plunger when said coil is excited enclosing a cone angle of less than 10°, to form an internal cone for controlling the first gap.
 14. A solenoid plunger magnet according to claim 9, wherein when viewed in the axial direction, the first air lies approximately in the center of said coil.
 15. A solenoid plunger magnet according to claim 9, wherein said first plunger face and said first yoke counter-face are conical so as to form an internal cone control.
 16. A solenoid plunger magnet according to claim 9, wherein the outer diameter of said coil has a ratio of approximately 1:1 to the diameter of the second air gap. 